In recent years, systems have grown popular which include a camera mounted on a vehicle and provide a driver with an image of a vehicle periphery which can easily be a blind spot.
In particular, recently, systems such as the followings have been put to practical use: a system which provides an overhead image viewed from right above a vehicle and obtained through coordinate transformation of an image taken by a camera, and a system which has multiple cameras mounted on a vehicle, and provides a 360° image of a vehicle periphery by combining overhead images obtained by the coordinate transformation.
Such systems which combine images taken by multiple cameras into a single image have a problem that a composite image brings a feeling of strangeness because brightness is discontinuous at seams of images due to a type difference among cameras which constitute the system. Even with cameras of the same type, this problem also happens because the cameras differently work in automatic exposure correction, or a light amount decreases in proportion to a distance from the center of each camera.
To solve such a problem, techniques have been conventionally proposed which correct brightness of images taken by respective cameras so that image areas taken in common by adjacent cameras can have the same average brightness, and display the brightness-corrected image. (Patent Document 1, Patent Document 2)